Chemokines have been implicated in the neuropathogenesis of AIDS and neuro-inflammatory disorders. However, as both neuronal and non-neuronal cells express chemokine receptors in the CNS, it is unclear to what extent cell type-specific receptors mediate the effects of chemokines on neurons. There is also controversy about the possibility that chemokines may be beneficial or toxic for neurons in various physiological and pathological conditions, their action being affected by the activity of other endogenous systems, such as those for opioids. Our research aims to determine the direct effects of chemokines on neurons independently of their action on inflammatory and glial cells, and identify the molecular mechanisms that regulate the activity of neuronal chemokine receptors including their interaction with major neurotransmitter and neuropeptide systems. This application will study the involvement of neuronal chemokine receptors in the survival of pure populations of rat and human neurons. The hypothesis suggested by our preliminary data is that these receptors play an important role in supporting neuronal survival and that their abnormal activation results in neuronal death. To test this hypothesis, the question of whether individual chemokine receptors (i.e. CXCR4) may couple to both neurotrophic and neurotoxic pathways will be addressed first. To this end, the interaction of neuronal CXCR4 with the neurotoxic HIV-1 protein gp120 will also be studied. Thus, the ability of chemokines and gp120 to induce receptor phosphorylation, dimerization and desensitization in various experimental conditions will be investigated. Differences in the molecular activation/deactivation of chemokine receptors, upon binding to chemokines and gp120 will be examined, to evaluate whether this may lead to recruitment of different effectors with opposite results on neuronal survival. Finally, the modulation of chemokine receptor function and expression by glutamate and opioids will be studied, to test the possibility that an alternative or additional level of regulation is exerted by the simultaneous activation of these systems, altering the effect of chemokines on neuronal signaling and survival. Biochemical, molecular biological, pharmacological and imaging approaches will be employed to study the activation of chemokine receptors and test their effect on the intracellular pathways involved in neuronal survival and apoptosis. These studies will help us understand the physiological role of chemokines in the CNS and their involvement in HIV neuropathology, neuroinflammatory diseases as well as in the neuropathology associated to drug abuse.